X-ray topography apparatus

ABSTRACT

This invention provides an improvement in an X-ray topography apparatus for photographing grid distortions of a monocrystalline solid body. In the X-ray apparatus which includes a rotary oscillatory drive in communication with its feed line, the crystalline body to be examined is oscillated along the feed line about an axis in the plane of the feed line and perpendicular to said plane formed by the inciding and refractory X-rays of the apparatus with the crystalline body, the amplitude of the rotary oscillation being set to a sufficiently low value to maintain the level of X-ray diffraction constant, and the improvement comprising an electronic follow-up device in direct communication with the oscillatory drive to continuously readjust the zero point of the oscillation to provide a maximum intensity of the diffracted X-ray beam recorded.

United States Patent Grienauer Aug. 7, 1973 X-RAY TOPOGRAPHY APPARATUS Siemens Aktiengesellschatt, Berlin and Munich, Germany Filed: Oct. 20, 1971 Appl. No.2 190,722

[73] Assignee:

[30] Foreign Application Priority Data Oct. 20, 1970 Germany P 20 15 51 L] References Cited UNITED STATES PATENTS 4/1958 Chope 250/83 C 3/1969 Kevey 250/375 4/1965 Hague, Jr. et al. 250/515 Primary Examiner-James W. Lawrence Assistantfixgginer-B. C. Anderson Attorney-Carlton Hill, J. Arthur Gross et al.

[57} ABSTRACT This invention provides an improvement in an X-ray topography apparatus for photographing grid distortions of a mono-crystalline solid body. In the X-ray apparatus which includes a rotary oscillatory drive in communication with its feed line, the crystalline body to be examined is oscillated along the feed line about an axis in the plane of the feed line and perpendicular to said plane formed by the inciding and refractory X- rays of the apparatus with the crystalline body, the amplitude of the rotary oscillation being set to a sufficiently low value to maintain the level of X-ray diffraction constant, and the improvement comprising an electronic follow-up device in direct communication with the oscillatory drive to continuously readjust the zero point of the oscillation to provide a maximum intensity of the diffracted Xray beam recorded.

I Claims 6 Drawing figures DIFFERENTIAL AMPLIFIER I GENERATOR 1,1

OSCILLATORY MOVEMENT TRANSMITTER PATENTEL 3.751.662

sum 2 or 2 i v INVENTOR He/nP/ch Gr/enau er ATTYS.

X-RAY TOPOGRAPHY APPARATUS BACKGROUND OF THE INVENTION This invention relates to an X-ray topography apparatus for photographing crystallographic imperfections of a mono-crystalline solid body having deformations in its crystal-lattice plane. More particularly, the invention relates to a topography apparatus in which the crystalline body to be examined is oscillated by a rotary oscillatory drive about an axis in the plane of the feed line of the apparatus and perpendicular to said plane which is formed by the inciding and refractory X-rays of the apparatus with the crystalline body.

The use of X-ray topography apparatuses for the examination and filming of imperfections in moncrystalline semi-conductor disks is well known in the art. In these devices, generally a semi-conductor disk is radiated with a well collimated xrray beam. In order to X-ray the entire surface of the disk it is moved at an invariable angle between the surface of the disk and the inciding beam of the X-ray apparatus in a direction perpendicular to the width of the beam. In the apparatus, a film is provided which is moved parallel to and in the same direction as the film on a surface spaced from the feed line on which the disk is moved. Generally, the distribution of intensity of the radiation provided by the disk, which has been diffracted substantially at the crystal-lattice plane placed perpendicularly to the surface, is determined by the degree of blackening of the film. The film is arranged to move parallel to the disk at the same speed, whereby the diffracted capacity of the interior of the semi-conductor disk is recorded on the film upon passing the disk below the flat beam of an X-ray for each surface element.

Because the intensity of the X-ray radiation of the grid distortions depends on the mechanical tensions in the semi-conductor material positvely connected therewith, it is possible to obtain with the X-ray topography apparatus an exact image of thelocal distribution of the grid defects in the semi-conductor disks, such as dislocations, crystalline disturbances, twin formations, slip bands and the like.

In the use of these known X-ray topography apparatuses, there is a problem particularly in the inspection of semi-conductor disks which were subjected after their production to further treatment, eg a thermal effect by a diffusion process, of the originally extremely plain disks showing distortions. Such distortions are extremely troublesome and difficult to locate by an X-ray topography apparatus as they are only noticeable by a change of the angle of incidence. However, it is important the angle of incidence be maintained constant because in viewing the low angular splitup of the individual X-ray lines, eg the K alpha, and K alpha, lines, a sharp directional collimating is necessary in the diffracted radiation.

In an attempt to overcome the erroneous results caused by the angle changes resulting from the distortions of the surface of the disks, means have been provided in X-ray topography appatuses to oscillate the crystal while it was being photographed. The crystal is oscillated about an axis in the plane of the feed line and perpendicular to the plane which is formed from the inciding and diffracted X-rays of the apparatus with the crystalline body being examined. The axis of rotation in the plane of the feedline is, thus, located in each examination at the point or location of the semiconductor where it is being radiated at that particular time. With this arrangement, the amplitude of the rotary oscillation is so large that the entire range of possible angle changes is included as a result of the distortions of the surface of the disk. The magnitude of this amplitude is either predetermined or determined by preceding measurements of individual amplitudes on the disk. Generally, the amplitude values range up to about plus or minus l.5.

Another problem in connection with the large amplitude required in the known topography apparatuses resides in the fact that due to the low dispersion width of 2 to 3 minutes of the diffracted X-ray lines and the necessary sharp focusing for photographing the crystal, only a small fraction of the entire radiation time of a surface element is available as the actual exposure time of the film. 'In addition, there is the disadvantage of the diffracted intensity of additional X-ray lines, for example, the K alpha: line which in relation to the K alpha, line has an angle difference of 2 minutes, is recorded in addition to the K alpha, line.

In order to eliminate the influence of the additional X-ray lines, it has been proposed to maintain the amplitude of the rotary oscillations so low that the desired X-ray line is not abandoned completely. As a result of this procedure, only the desired X-ray line can pass through the second stationary slit as diffracted radiation. In order to be able to examine each point of a distorted semi-conductor disk, it is'necessary then to effeet a new orientation of the surface of the disk with reference to the inciding radiation. For that purpose, the distortion would have to be photographed prior to the actual inspection of the disk, in order to provide a program for the new focusing in each subsequent case.

In view of the topography apparatuses described, there is a need for an apparatus designed to operate at a low amplitude of the rotary oscillations of the crystal without requiring any interruption for determining the distortions of the crystal. This X-ray topography apparatus should be designed to be applicable for series controls in production, i.e. mass production.

SUMMARY OF THE INVENTION 1 have, accordingly, developed an X-ray topography apparatus which overcomes the problems of the known X-ray topography apparatuses. In my X-ray topography apparatus having a rotary oscillatory drive in direct communication with its feed line, the crystalline body to be examined is oscillated along the feed line about an axis in the plane of the feed line and perpendicular to said plane formed by the inciding and refractory X- rays of the apparatus with the crystalline body, the amplitude of the rotary oscillation being set to a sufficiently low value to maintain the level of X-ray diffraction constant, and the improvement comprising an electronic follow-up device in direct communication with the oscillatory drive to continuously readjust the zero point of the oscillation to provide a maximum intensity of the diffracted X-ray beam recorded.

The electronic follow-up device provided by the present invention continuously compensates the distortion angle or angle of movement of the crystal being examined so that the theoretic value of the angle of incidence is maintained for the X-ray at the center position of the crystal.

It is therefore an object of the present invention to provide in an X-ray topography apparatus having an electronic follow-up device for compensating the angle of distortion of the crystal being photographed for imperfections in its crystal-lattice.

Other objects, features and advantages of the present invention will be readily apparent from the following description of the preferred embodiments thereof taken in conjunction with the accompanying drawings, although variations and modifications may be effected by those skilled in the art without departing from the spirit and scope of the novel concepts of the present invention as defined in the appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic view of an X-ray Topography apparatus having an electronic follow-up device embodying the present invention;

FIG. 2 is a schematic view illustrating the oscillation system of the topography apparatus schematically shown in FIG. 1, illustrating the oscillation of a crystalline disk;

FIG. 2A is a partial side view of the present oscillation system taken along line IIII of FIG. 2;

FIG. 3 is a joint circuit diagram for the electronic integrator and differential amplifier of the electronic follow-up device schematically shown in FIG. 1;

FIG. 4 is the principal circuit diagram of the impulse generator of the electronic follow-up device schematically illustrated in FIG. 1; and

FIG. 5 is a detailed circuit diagram of one of the electronic phases illustrated in FIG. 4.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to FIG. I initially, there is shown schematically an X-ray topography apparatus having an electronic follow-up device embodying the present invention. The X-ray topography apparatus comprises an X-ray source 2 which focuses by means of a collimator 3 and a slotted diaphragm 4, an X-ray radiation 5. The X-ray radiation 5 is a flat ray (surface not shown) which extends to a semi-conductor crystal 1 at an incident angle predetermined by the arrangement of the apparatus.

The disk 1 is placed on a feed or conveyor belt 11 and is moved from left to right in the direction shown by the arrow 14. The disk 1 diffracts an X-ray radiation 6 which passes through the slot of a diaphragm 8 and is recorded on a film 10 as blackening. As shown, the film 10 is synchronously moved in the same direction as the disk 1 on a feed or conveyor belt 12 parallel to and below the conveyor belt on which the disk 1 is moved.

The fiat X-ray 5 scans a strip on the surface of the disk I corresponding to its own vertical width. It is preferred to have the vertical width of the fiat X-ray 5 large enough so that it will cover and include the entire disk I. The synchronous feed of the disk 1 and film 10, assures the film 10 to be able to furnish a precise overall picture of the local conditions ofintensity for the entire disk 1. The diffracted radiation of an X-ray line other than the desired one is identified by a broken line 15. As can be seen, the radiation of this undesired X-ray line is prevented from exposing the film 10 by the diaphragm 8.

In FIG. 2, the oscillating system for oscillating and rotating the disk 1 along the feed line is shown. The oscillation system comprises a support 27 on which the carrier 111 for the disk, is supported. As shown in FIG. 2A, the support 27 is an L-shaped structure which has in its upright portion, a peg 121 which forms the axis 21. The support 27 can be rotated around this peg 121 so that the crystalline disk 1 only carries out rotary movements corresponding to the oscillation angle with respect to axis 21. It is conventional to glue the crystalline disk 1 to the base plate or carrier by means of a beeswax. The support 27 is caused to move upward and downward in an oscillating manner by a motor 25 and a crank drive 24. As shown, the motor 25 with its oscillation disk 125 and crank 26 propels the support 27 for the carrier 111 to rotate about the axis 21 in a plane of the feed line and on the disk I. By shifting the motor 25 in the direction of the double arrow 28, the zero point position can be varied for the rotary oscillations.

As shown in FIG. 2, the axis 21 is placed perpendicularly to the surface formed by the X-rays 5 and 6. The curved arrow 22, illustrates the oscillating movement of the crystalline disk 1 on the carrier 111. As can be seen, the location of the axis 21 remains constant in relation to the X-rays 5 and 6, as the disk is moved further, and thus passes through the disk 1.

A distortion which may occur in disk 1 is indicated with great exaggeration in FIG. 2 by the reference numeral 23. As indicated, such a distortion acts upon further movement of the disk in the forward direction identified by the arrow 14 as a steady change of the angle of incidence of the X-ray radiation 5 upon the surface of the disk 1.

The electronic follow-up system according to the present invention makes it possible for the zero point of the oscillations about the axis 21 to be continuously readjusted during the forward movement of the disk. The zero point position is readjusted in proportion to the size of the variation of the angle of the normal line of the surface of the disk at the location the X-ray 5 radiates the disk 1. Thus, no matter how the disk 1 is moved on the feed line, the surface of the disk will always be flat with respect to the X-ray radiations.

The electronic follow-up device includes a counting tube 16 for the continuous control of the intensity of the reflected X-ray radiation 6, as schematically illustrated in FIG. 1. In addition, the electronic device includes an electronic integrator 31, electrically connected to the output of the counting tubes 16, a differential amplifier 32 electrically connected to the output of the integrator, an impulse generator 41 electrically connected to the integrator, an oscillatory movement apparatus 51, for generating the oscillatory movements of disk 1, controllable by the differential amplifier 32. The double arrow 52, drawn in a broken line, as shown in FIG. 1, indicates the mechanical-electrical coupling e.g. an electric wires between the apparatus 51 and the drive for the oscillation movement of the disk 1. which is an electrical connection such as a copper wire leading from the apparatus 51 to the pump 25 As shown in FIG. 1, as the X-ray radiation 6 passes through the film 10 almost unattenutated as an X-ray beam and into the counting tube 16, a diaphragm 17 is provided on the end of the counter to assure that only the radiation which was recorded by the film 10 enters the counting tube 16.

The electrical impulses released in the counting tube 16 are transmitted to the electronic integrator 31, then to the differential amplifier 32 and then to the apparatus 51 from where the electrical impulse is generated to the oscillating system for generating the oscillatory movements of disk I as illustrated in FIG. 2. That is, the oscillatory movements are controlled by the electronic impulses generated by the electronic follow-up device as received through the diffracted X-rays 6 from the disk 1.

In FIG. 3, there is shown a joint circuit diagram of the electronic integrator 31 and of the differential amplifier 32. The signal originating from the counting tube 16, is supplied from the connecting terminals 33 by way of relay contacts and b which are alternately closed, to the associated capacitors 35 and 135 which are connected by wires 50 to the terminal connectors 33. Upon closing the relay contacts C which switch simultaneously, the electric charges stored during the closing phase of contacts a, and b,, respectively, in capacitors 35 and 135, are fed to the two inputs of the differential amplifier 32. The circuit is prepared for recording a new formation of a differential by way of the relay contacts d. which are switched jointly. An output 39 is provided for the control signal formed in the differential amplifier 32 and to be transmitted to the apparatus 51 which in turn generates the control signal to the oscillator, as shown in FIG. I. In order to avoid any errors by any statistical fluctuations, the contacts a 4 and b are closed in each case for at least several seconds, preferably for about four seconds. As shown in FIG. 3, the contacts 0, b etc, are all within the electronic integrator 31 and amplifier 32 does not have any contacts. The zero point position is determined separately and is adjusted by hand. Only then does the device according to the present invention operate automatically. For the following of the zero point, the crystal is always turned in such a way in respect to the striking X-ray beam 5 that the differential point which beam 5 hits seems to be vertical. The oscillating rotary motion serves the purpose to create a control signal for the follow-up of the zero point. Thus, the device is arranged to move the crystal to the zero point at any time desired.

FIG. 4 shows the circuit diagram of an impulse generator circuit 41, according to the present invention. As shown, the circuit comprises five monostable multivibrators 42, 43, 44, 45 and 46. The multivibrators are interconnected electrically and functionally by means of the relays A, B, C, D and E and their contacts a,, b,, c,, d,, e,, 0 b 0,, d e, and (1 b 0 d, and e After a short application of contact by the starter 66, as shown in FIG. 4, the contacts a and b, are closed by energizing relay A. Because of a delayed action circuit in multivibrator 43, relay B is energized after a short period of time. Accordingly, the contacts 1;, and b, are closed and contact b, is opened. The opening of b; terminates the energizing of relay A, whereby contact 0 is opened again. The closing of contact 12 within a predetermined period of time, effects the energizing of relay C in phase 44 and the opening of contact e in phase 43. Due to the electrical-functional connection of the individual phases, a starting impulse once applied cyclically passes within the predetermined period of time through phases 42, 43, 44 and 45 to phase 46, and back to phase 42.

In FIG. 5, there is shown a detailed circuit diagram for one of the monostable multivibrators of the phases 42, 43, etc., illustrated in FIG. 4. The capacitor 71 and the resistors 72 form the RC member together by having capacitor 71 discharged by means of the transistor 73 with the time constant adjustable at the resistor 72. The discharge of capacitor 71 opens the transistor 74 whose current causes relay B to be energized.

In general operations of the electronic follow-up device, the contacts a, and b, of the electronic integrator, as shown in FIG. 3, are closed for a predetermined period of time consecutively for an equally long period of time for charging the capacitors 35 and 1-35. A charging of the two capacitors in different magnitude of times means, during the time gap, the adjustment angle of disk 1 is extended beyond the maximum and must be readjusted. This readjustment is supplied by way of the output 39 of the differential amplifier 32, to the apparatus 51 in accordance with the diffeorential signal formed in the amplifier 32.

The X-ray topography apparatus with the electronic follow-up device as described above, is particularly useful in manufacturing operations for quality control in production. The present apparatus provides an exact knowledge of the locations where crystalline imperfections exist in a semi-conductor disk as described above, and the individual elements to be produced from a disk, eg for a construction element with an integrated circuit, can be sorted out and excluded, if necessary, from the subsequent production process of the desired elements, or products.

I claim as my invention:

1. An X-ray topography apparatus for photographing crystalline imperfections of a mono-crystalline solid body having deformations in its crystal-lattice plane, which apparatus includes a rotary oscillatory drive in communication with its feed line to oscillate the crystalline body to be examined along said feed line about an axis in the plane of the feed line and perpendicular to said plane formed by the inciding and refractory X- rays of the apparatus with the crystalline body, the amplitude of the rotary oscillation being set to a sufficiently low value to maintain the level of X-ray diffraction constant, and a film which is moved synchronously with the crystalline body in parallel manner therebelow to record the X-rays diffracted from the crystalline body, the improvements comprising an electronic follow-up device in direct communication with the oscillatory drive to continuously readjust the zero point of the oscillation, the initially adjusted position at which the X-rays hit the crystalline body, to provide a maximum intensity of the diffracted X-ray beam recorded.

2. An X-ray topography apparatus according to claim 1, wherein the electronic follow-up device comprises a counting tube to measure the intensity of the X-ray beam, an electronic integrator electrically connected to the output of the counting tube, a differential amplifier electrically connected to the output of the integrator and an impulse generator electrically connected to the integrator whereby the impulses released from the impulse generator open and close the contacts of the integrator.

3. An X-ray topography apparatus according to claim 2, wherein the electronic integrator consists of two capacitors placed placed parallel to the input of the integrator, separated from each other by relay switch contacts and electrically connectable.

4. An X-ray topography apparatus according to claim 3, wherein the circuit of the impulse generator comprises five monostable multivibrators, said multivibrators each having a relay and being interconnected electrically by operating relay contacts. 

1. An X-ray topography apparatus for photographing crystalline imperfections of a mono-crystalline solid body having deformations in its crystal-lattice plane, which apparatus includes a rotary oscillatory drive in communication with its feed line to oscillate the crystalline body to be examined along said feed line about an axis in the plane of the feed line and perpendicular to said plane formed by the inciding and refractory X-rays of the apparatus with the crystalline body, the amplitude of the rotary oscillation being set to a sufficiently low value to maintain the level of X-ray diffraction constant, and a film which is moved synchronously with the crystalline body in a parallel manner therebelow to record the X-rays diffracted from the crystalline body, the improvement comprising an electronic follow-up device in direct communication with the oscillatory drive to continuously readjust the zero point of the oscillation, the initially adjusted position at which the X-rays hit the crystalline body, to provide a maximum intensity of the diffracted X-ray beam recorded.
 2. An X-ray topography apparatus according to claim 1, wherein the electronic follow-up device comprises a counting tube to measure the intensity of the X-ray beam, an electronic integrator electrically connected to the output of the counting tube, a differential amplifier electrically connected to the output of the integrator and an impulse generator electrically connected to the integrator whereby the impulses released from the impulse generator open and close the contacts of the integrator.
 3. An X-ray topography apparatus according to claim 2, wherein the electronic integrator consists of two capacitors placed placed parallel to the input of the integrator, separated from each other by relay switch contacts and electrically connectable.
 4. An X-ray topography apparatus according to claim 3, wherein the circuit of the impulse generator comprises five monostable multivibrators, said multivibrators each having a relay and being interconnected electrically by operating relay contacts. 